THERMOTROPIC POLYESTERS - THERMAL TRANSITIONS AND POLYMORPHISM OF POLY(4-OXYBENZOATE-CO-1,4-PHENYLENE ISOPHTHALATE)S

Differential scanning calorimetry and wide-angle X-ray diffraction tec hniques are employed to investigate the melting behaviour and crystall ine structure of poly(1,4-phenylene isophthalate) and poly(4-oxybenzoa te-co-1,4-phenylene isophthalate) containing equimolar quantities of t he constituent 4-oxybenzoyl, 1,4-phenylenedioxy and isophthaloyl units . These materials can contain two different crystalline structures, bo th consisting of 1,4-phenylene isophthalate sequences. The formation o f these polymorphs in both the homopolymer and copolymer is influenced by the crystallization and/or annealing conditions. The melting behav iour of the copolymer is strongly influenced by annealing, but these c hanges can be reversed by remelting. Consequently, they are not caused by changes in chain constitution arising from transesterification.